Oxygen flush die casting method and apparatus

ABSTRACT

The invention is directed to a die casting method and apparatus wherein the shrinkage pores are concentrated in the unimportant regions of the product by positively retarding solidification of the cast metal in those regions so that the strength defects may be reduced in essential regions of the resultant product.

ilniie States aieni [1 1 Mild [451 Aug. 14, 1973 OXYGEN FLUSH DIE CASTING METHOD AND APPARATUS Isao Miki, Fuji, Japan Nippon Light Metal Company Limited, Tokyo, Japan Filed: July 13, 1971 Appl. No.: 162,153

Inventor:

Assignee:

Groteke 164/120 X 3,106,002 10/1963 Bauer 164/120 3,672,440 6/1972 Miura et al. 164/136 X FOREIGN PATENTS OR APPLICATIONS 224,008 11/1968 U.S.S.R 164/55 Primary Examiner-J. Spencer Overholser Assistant Examiner-John E. Roethel Attorney-William J. Daniel ABSTRACT The invention is directed to a die casting method and apparatus wherein the shrinkage pores are concentrated in the unimportant regions of the product by positively retarding solidification of the cast metal in those regions so that the strength defects may be reduced in essential regions of the resultant product.

9 Claims, 7 Drawing Figures Patented Aug. 14, 1973 2 Sheets-Sheet l FIG.2

FIG.3 FIG.4

Patented Aug. 14, 1973 3,752,213

2 Sheets-Sheet 2- OXYGEN FLUSH DIE CASTING METHOD AND APPARATUS This invention relates to an oxygen flush pressure die casting method and apparatus and more particularly to an improved oxygen flush pressure die casting method and apparatus adapted to produce sound cast products substantially free of structural defects by causing the shrinkage pores to be concentrated in unimportant or non-essential regions which of the casting product, can either be removed after casting or do not require substantial strength during use of the product.

The pressure die casting method is a very effective casting method for efficient mass production of cast products having beautiful casting surface and high dimensional accuracy. According to the conventional pressure die casting methods, however, air entrapped in the molten metal during its injection into the die cavity appears in the form of blow holes in the final cast product. Therefore, cast products thus obtained are more or less defective in mechanical strength and unsuited for use for machinery part, structural members or the like which require high strength reliability.

In the oxygen flush pressure die casting method, injection casting of molten metal is carried out by introducing oxygen gas into the die casting apparatus to displace air present beforehand in the die cavity and injection passageway, such as the injection sleeve and runner. According to this method, oxygen gas entrapped in the injected molten metal immediately reacts with the molten metal to become fine metal oxide particles in the cast product, so that the final cast product is almost free from blow holes.

However, cast products obtained by this oxygen flush pressure die casting method tend to be subject to the formation of relatively large shrinkage pores, as compared with products obtained by the conventional die casting method. Therefore, the improvement achieved in the oxygen flush pressure die casting method is offset by these large shrinkage ports.

In general, the molten metal injected into a die cavity tends to shrink on solidification and tends to form the shrinkage pores in those regions where the solidification is retarded or occurs last in point of time. In a conventional die casting method, air entrapped in the injected molten metal is dispersed and therethrough in the form of numerous compressed air bubbles which expand to some extent as the metal solidifies and shrinks the formation of shrinkage pores being thus prevented by the extent of expansion of the bubbles. In the oxygen flush pressure die casting method, on the other hand, only a small amount of bubbles remain in the molten metal and thus compensation cannot take place so that the shrinkage pores caused by the solidification and shrinkage of the molten metal are presumably created in the same way and in the same areas of the cast product as before.

The present invention is based on the observation that in cast products obtained by the oxygen flush pressure die casting method, large shrinkage pores appear concentrically in the regions of the product where the solidification is relatively retarded and directed to an improvement in the above oxygen flush pressure die casting method wherein the die assembly, which consists of a fixed die and a movable die, is deliberately provided with the heat-insulated zones in certain die w'all regions, preferably on each side of the die which are contiguous to unimportant or non-essential parts of the final cast product which part can eventually be removed by mechanical means, when required to contribute to the mechanical strength of the product during use can be left in place. Thus, the molten metal injected into the die cavity has its solidification retarded in each region in contact with each insulated zone compared to the rate of solidification in other portions of the molten metal, so that most of the shrinkage pores are confined to the unimportant parts of the cast product, while shrinkage pores are avoided in other important parts of the cast product which are required to contribute to mechanical strength during use.

The heat-insulated zones can be formed in the die wall by providing appropriate recesses in the die wall and fitting in each of these recesses an insert element made of ceramic or like non-heat conductive material and having a shape corresponding to the recess, or a metallic insert element shaped in cross-section to provide gaps or clearance spaces between the die wall and the insert element surface after completion of the fitting. The heat-insulating elements may be modified by providing heating wires embedded therein and connected to a current source so that the zones in question can be positively heated to more effectively carry out the method of the present invention.

Therefore, an object of the present invention is to provide an improved oxygen flush pressure die casting method wherein any shrinkage pores-are concentrated in the unimportant areas of theproduct which do not require particular strength.

Another object of the present invention is to provide an improved oxygen flush pressure die casting method for producing the sound casting products substantially free of impermissable strength defects caused by the shrinkage pores and blow holes.

The present invention shall be explained in more detail with reference to the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view showing the principal parts of one illustrative type of die casting apparatus for carrying out the die casting method according to the present invention and designed, for example, to cast a side-cover of a housing for small electric motor.

FIG. 2 is a sectional view of the die casting apparatus taken along the line IIII in FIG. 1.

FIG. 3 is a longitudinally sectional view of a product made according to the die casting apparatus shown in FIG. 1 and showing the condition of the product immediately after completion of casting.

FIG. 4 is a longitudinally sectional view of the same product as shown in FIG. 3, but showing the final condition thereof after finishing to remove the nonessential areas therefrom.

FIG. 5 is a sectional view showing a heat-insulated zone formed in the die wall.

FIG. 6 is a sectional view showing a modification of the heat-insulated zone shown in FIG. 5.

FIG. 7 is a sectional view showing a still another embodiment of the heat-insulated zone shown in FIG. 5.

Referring to FIGS. 1 and 2, the die casting apparatus shown there comprises a die plate 1, a fixed die 11 attached to the die plate 1, and a movable die 12 which is brought in close contact with the fixed die 11 by operation of die clamping pistons 3, so that when the fixed die 11 is bodily contacted with the movable die 12, a

split-die may be formed, in which a die cavity 4 of a desired shape and a connecting runner 5 having a narrow cross-section. A molten metal injecting sleeve 6 extends through the die plate 1 and serves to inject molten metal M poured therein into the die cavity 4 through runner 5 by operation of a plunger 7 which reciprocates along the inside wall of the sleeve. The sleeve 6 is provided on its upper side with a molten metal inlet 8. An oxygen feeding nozzle 9 is arranged to be inserted in the molten metal inlet 8.

Formed in localized sections of the die wall are heatinsulated zones 10 which correspond to the locations of bolt-holes It) or rotor holes 10" of the product, as shown in FIG. 4, which holes are intended to be removed after completion of the casting.

FlGS. S, 6 and 7 show, respectively, several embodiments for the heat-insulated zone formed in the die wall.

in FlG. 5, the heat-insulated zone is formed by an insert element 13 made of ceramic material (such as fire brick, porcelain, castable refactory material, etc.) which is fitted into a corresponding recess 14 provided in advance in the die wall.

FIG. 6 shows a modification of the heat-insulated zone, and here an inserting element 15 is made of me tallic material in the cross-sectional shape of a flanged spool so as to provide insulation space 16 between the die wall 14 and the element 15 when the element 15 is fitted in the recess in the die wall.

In FIG. 7, still. another modification of the heatinsulated zone is shown where the embedded insert element 17 is provided with an electrical resistance heater core 13 in its interior. The heater core serves to positively heat the heat-insulated zones 10, thereby retarding effectively solidification of the contiguous regions of molten metal.

According to the method of the present invention, air present in the sleeve 6, runner S and die cavity 4 is displaced in advance with oxygen gas fed into the sleeve 6 through the nozzle 9, molten metal is then poured into the sleeve 6 from the molten metal inlet 8, and plunger 7 is operated to eject the molten metal within the sleeve into the die cavity 4 through the runner 5, wherein most of oxygen gas entrapped in the molten metal at the time of ejection thereof reacts immediately with the molten metal to produce fine metal oxide particles dispersed in the molten metal, thereby considerably reducing the number of the pores in the cast product.

Furthermore, the regions of the molten metal which are in contact with the insulated zones 10 solidify at very slower rate compared with the rate of solidification of the other regions of the molten metal. Therefore, as indicated in FIG. 3, the shrinkage pores are confined to those regions of the metal body as defined by the dotted lines in FIG. 3 which are in contact with the insulated zones 10. In the product in question, these regions correspond to the location of holes which are drilled therein. Hence, the pore-containing regions are eventually removed after completion of the casting, so that a sound product substantially free of blow holes and shrinkage pores can be obtained.

The foregoing description of the present invention is directed to an embodiment of the method designed for casting the product in which certain sections are intended to be removed after completion of the casting. However, the method of the present invention can also be applied to the casting of other types of products. For example, when casting products which include regions where no particular strength is required during use, the die wall with the heat-insulated zones can be employed in the same manner as in the foregoing embodiment so that any shrinkage pores will be concentrated within the portions of the product where no particular strength is required, thereby giving products having a high reliability in strength in its essential regions.

As can be seen from the foregoings products can be made according to the method of the present invention with a high reliability in strength, suitable for use as machinery parts or structural members, since the blow holes and shrinkage pores are not provided in the portion of the product where strength is important or essential.

What we claimed is:

1. In an injection die casting method wherein after the die cavity is flushed with oxygen gas, molten metal is injected into said cavity and permitted to solidify, the improvement comprising the step of selectively retarding the rate of solidification of at least one predetermined section of the metal mass in said cavity whereby shrinkage pores in the final cast product are substantially concentrated in such predetermined sections.

2. The method of claim 1 wherein each such predetermined section of said metal mass corresponds to a section which does not contribute to the essential mechanical properties of said final cast product.

3. The method of claim 3 wherein said rate of solidification is retarded in each said selected section and corresponding generally to the shape of said section.

4. The method of claim 1 wherein said rate of solidification is retarded in each of said selected sections by positively heating each such selected section.

5. The method of claim 1 wherein said predetermined sections correspond to portions of the cast product which are ultimately removed by a mechanical means after completion of the casting.

6. An injection die casting apparatus comprising two die plates together defining a die cavity, said plates being relatively movable to separate and close the same, means for flushing said die cavity with oxygen gas in advance of injecting said molten metal therein, means for injecting molten metal into said die cavity, and means for selectively retarding the rate of cooling of predetermined opposed corresponding surface areas of said two die plates whereby at least one section of the metal mass injected into said cavity situated between said opposite die surface areas is caused to cool at a slower rate than the remainder of said metal mass and shrinkage pores are concentrated within said slower cooled section.

7. The apparatus of claim 6 wherein said cooling retarding means comprises heating means embedded in at least one of said corresponding die surface areas.

8. The apparatus of claim 6 wherein said cooling retarding means comprises heat-insulating inserts formed of non-heat conductive material fitted in recesses provided in said opposed areas of said die plates.

9. The apparatus of claim 6 wherein said cooling retarding means comprises inserts made of metallic material fitted in recesses provided in said opposed areas of said die plates, said inserts being insulated from the remainder of said die plates by a clearance space extending substantially therearound.

a :1: :e t =2: 

1. In an injection die casting method wherein after the die cavity is flushed with oxygen gas, molten metal Is injected into said cavity and permitted to solidify, the improvement comprising the step of selectively retarding the rate of solidification of at least one predetermined section of the metal mass in said cavity whereby shrinkage pores in the final cast product are substantially concentrated in such predetermined sections.
 2. The method of claim 1 wherein each such predetermined section of said metal mass corresponds to a section which does not contribute to the essential mechanical properties of said final cast product.
 3. The method of claim 1 wherein said rate of solidification is retarded in each said selected section and corresponding generally to the shape of said section.
 4. The method of claim 1 wherein said rate of solidification is retarded in each of said selected sections by positively heating each such selected section.
 5. The method of claim 1 wherein said predetermined sections correspond to portions of the cast product which are ultimately removed by a mechanical means after completion of the casting.
 6. An injection die casting apparatus comprising two die plates together defining a die cavity, said plates being relatively movable to separate and close the same, means for flushing said die cavity with oxygen gas in advance of injecting said molten metal therein, means for injecting molten metal into said die cavity, and means for selectively retarding the rate of cooling of predetermined opposed corresponding surface areas of said two die plates whereby at least one section of the metal mass injected into said cavity situated between said opposite die surface areas is caused to cool at a slower rate than the remainder of said metal mass and shrinkage pores are concentrated within said slower cooled section.
 7. The apparatus of claim 6 wherein said cooling retarding means comprises heating means embedded in at least one of said corresponding die surface areas.
 8. The apparatus of claim 6 wherein said cooling retarding means comprises heat-insulating inserts formed of non-heat conductive material fitted in recesses provided in said opposed areas of said die plates.
 9. The apparatus of claim 6 wherein said cooling retarding means comprises inserts made of metallic material fitted in recesses provided in said opposed areas of said die plates, said inserts being insulated from the remainder of said die plates by a clearance space extending substantially therearound. 